Stereotype mat



Jan. 29, 1963 F. J. s'rANczAK ETAL STEREOTYPE MAT 2 Sheets-Sheet 1 FiledMay 9, 1955 Jan. 29, 1963 F. J. sTANczAK ETAL 3,075,260

STEREOTYPE MAT Filed May 9, 1955 2 Sheets-Sheet 2 United States Patent O3,075,260 STEREOTYPE MAT Frank J. Stanczak, Easton, Pa., and Richard A.Wolterding, Neenah, Wis., assignors, by mesne assignments, toKimberly-Clark Corporation, a corporation of Delaware Filed May 9, 1955,Ser. No. 507,113 10 Claims. (Cl. 22-55) The present invention relatesgenerally to stereotype mats and is particularly concerned with animproved cornposite stereotype mat and backing and with certain methodsfor manufacturing such products. This application is acontinuation-in-part of our copending application Serial No. 349,352,filed April 17, 1953, now Patent 2,936,797, issued May 17, 1960.

In the usual process for making a stereotype mat, a paperboard mat orflong, as it is sometimes called, is laid, over a lockup containing thetype, engravings, and other printing elements which are to be reproducedin the stereotype plate. then subjected to heavy pressure, suicient topress the mat into the face of the lockup and provide a reproduction ofthe printing elements in the face of the mat. During the pressingoperation, a molding combination of cork, felt, or other suitablematerials is positioned intermediate the mat and the pressure element.

Following the pressing operation, the mat may be dried by a processwhich includes placing the imprintedv mat in a curved former and dryer,sometimes termed the scorcher. This forming and drying operationachieves several desirable results. Since the actual printing plate ismade by casting molten type metal against the curved mat as a matrix, itis necessary that the mat be completely dried prior to the castingoperation and that it be sufficiently hard and rigid to resist thecasting pressure. In addition, it is the current practice in variousprinting industries to shrink stereotype mats quite substantial amountsin order to reduce the size of the printed image and the amount of paperrequired in the printing operation. These two functions, i.e., thepreparation of the mat for the casting operation and the controlledshrinkage of that mat are accomplished during the drying operation.

The usual dryer for forming the mat receives the mat against a curved,foraminous surface, which is connected to a source of reduced pressurein order that the moisture and other vapors liberated during the heatingoperation will be drawn off through the back of the mat. When using ahigh shrink mat, it is normally desirable for the drying to be done intwo steps, in the first of which the mat is heated while still fiat todrive off some of the moisture and, in the second step, the mat isformed into a curved shape in the dryer mentioned above and is heatedunder vacuum conditions to drive olf the remaining moisture through theback of the mat. In this Way, the maximum shrinkage of the mat isachieved. In a low-shrink or a non-shrink mat the pre-drying step priorto placing the mat in the former is generally not required.

Since the forming and casting operations involve quite substantialpressures, it has been found necessary to provide some means forpreventing buckling or yielding of the mat in the nonprinting areas, andparticularly those areas which are of substantial dimensions. Inpractice, the most common means for packing or backing the mat consistsin attaching thin strips of paper felt along the rear surface of the matin those areas of the mat which have rather large nonprinting areas.This hand packing is usually done after the mat has been molded and, ifa pre-drying step is used, between the first drying and the final dryingagainst the curved former. Reinforcement of nonprinting areas too smallto be packed with felt The lockup with the mat in position is` 3,075,260Patented Jan. 29, 1963 strips is sometimes accomplished by running thepoint of a pencil on the back side of the mat in those areas to formnonplanar areas in the face of the mat which will resist buckling moreeectively.

Packing operations of the type mentioned above constitute a very seriousproblem in the newspaper field. Mat packing is inherently time consumingand costly and, of even greater importance, it must be done shortlybefore press time, when every minute is vital. Many of the pages of thenewspaper cannot be completed in the lock-` up until a few minutesbefore press time, either because it is desi-red to cover last minutedevelopments or because of the time necessary to complete thestereoplates that make up portions of the pages. Consequently, when suchpages are finally closed, and there may be many such pages in a largenewspaper, it is necessary that the stereotype mat be promptly finishedso that the plates for the presses can be cast and installed. At thispoint, the necessity heretofore for hand packing each of the mats hasbeen a serious deterrent to prompt completion of such mats. The handpacking operation is time consuming and requires the services of skilledworkmen who must use considerable judgment in selecting the areas to bepacked and in applying the packing material properly, in

order to render the packing effective for its intended purpose.Consequently, this type of packing represents a very substantailproportion of the time and cost involved in producing stereotype plates.Pages must be closed an appreciable length of time in advance of thetime set for operation of the press, and skilled workmen who might beotherwise engaged are required for the hand packing operation.

In the conventional process, the mat must be packed prior to the finalforming and drying operation, and the presence of the packing strips onthe back of the mat during this operation creates further seriousproblems in the production of satisfactory stereotype plates.Particularly when the packed stereotype mats are subjected to the heatin the former and dryer, the packing shrinks at a different rate and ina different amount than does the mat. In those areas where a largeamount of packing has been applied, the unequal shrinkage and/orslippage between the mat and the packing due to the heat of the dryermay cause the strips to overlap printing areas or otherwise distort themat. In addition, the packing strip with its adhesive layer does notpermit free passage of moisture and other vapors, and incomplete dryingand irregular shrinkage of the mat often occurs in heavily packed areas.These deficiencies in hand packed mats are particularly emphasized incolor printing wherein registration of the several mats bearing the sameimprint or reproduction is important. A slight variation in the mannerof packing the several mats required for a single reproduction in colormay seriously affect the registration of material reproduced from suchmats.

There is, therefore, a very great existing need for an improvedsteretotype making procedure, and especially for an improved mat packingmeans which will not impede the free passage of moisture and other vaporthrough the back of the mat during drying and which will shrinksubstantially to the same degree as the mat. This material should alsobe flexible both before and after drying, since the mat is subjected toconsiderable bending during use and must remain flexible during thetreatment in the former and dryer, as well as atthe time of thesubsequent pressure yduring ltherolling and pressing of the mat, poordefinition of the printing characters and a rough surface on the face ofthe printing Will result. The desirable mat backing material should alsobe adaptable for use in conventional `mat forming equipment and withVconventional technique.

The present invention Yhas for its principal 'object the provision ofstereotype making procedures and materials capable of meetingthe abovestated requirements. A more specific object of the invention is theprovision of an improved, composite stereotype mat and backing which canbe used without any need for subsequent packing of the non-printingareas, while maintaining the Vnormal vapor permeability necessary tothe'nal forming of the mat. A further object is to provide such acomposite mat wherein the shrinkage characteristics are compatible withexisting stereotype mat products of the shrinkage type.

Another object of the invention is to provide a backing materialsuitable for use in conjunction with known stereotype mats, which iscompletely moldable and bo-ndable with the mat to resist the moldingpressures, and so that it can resist the pressures encountered duringthe forming and drying operation so as to be properly set to provide aunitary mat element having adequate strength and rigidity to withstandthe pressures produced during the casting operation. Y

Still another object of the invention is to provide a ethod for theproduction of a nished stereotype matrix, whichmethod is considerablyfaster in operation and more economicalV than the conventional processof hand packing-stereotype mats now in use.

The various features of the invention and the specific manner in whichthe objects of the invention are accom-V plished will be made apparentin the following description and the accompanying drawings of certainillustrative embodiments of the invention.

In the drawings:

FIGURE l is a view, in perspective of a portion of a lookup or otherprinting element illustrating one manner inwhich the mat, the backing,and the blanket are arranged in the practice of the invention;

FIGURE 2 is a View in perspective of a composite mat unit in accordancewith the invention with theV backingV already attached;

FIGURE 3 is a fragmentary view in elevation of the assembly duringpressing or molding of the mat about the printing form and is`illustrative ofone method which may be used;`

FIGURE 4 is an enlarged cross-section view of a portion of the backedmat after its removalV from the moldiris press; Y

FIGURE 5 is a fragmentary view of the backed mat during itsformation inthe dryer; and

FIGURE 6 is aside elevational View of the backed mat in theform in.which it is received in a casting box.

Inl the practice of the present invention, a paperboard mat of the typenewV commonly used is provided with a backing consistingiof a pluralityof plies of creped, cellulosic tissues having dispersed therein athermally rigidiablebinder, exemplified in the 'preferred embodiment ofthis invention by'various thermosetting resins. A material of this typehas beenfound to be properly moldable iu'that it iscapa'ble ofV taking apermanent set in the printing areas of the mat, but still retains itsresiliency so as to provide the` desired bulk inthe portions overlyingthe nonprinting areas of the mat. Further advantages stem from the factthat the backing material, after hardening of the binder, has asubstantially increased tensile and,.of more importance,.a substantiallyincreased compressivel strengtha desirable feature during the castingoperation, but the mat is still quite iiexible so that it can conform tothe' curved surface of the casting box. One of the more remarkablecharacteristics of the backing whenapplied to a conventional stereotypemat is the fact that the shrinkage ofthe combined mat and backing whichfitakes place during scorching is very nearly the same as the unpackedmat itself.

The material which we employ for the backing has found extensive use inthe manufacture of filters and for various other purposes. The materialand its method of preparation are described in Catlin and Wollwage U.S.Patent No. 2,554,814, issued May 29, 1951. As described in that patent,the preferred material consists of a plurality of plies of thin, creped,cellulosic tissue having an air-dry basis weight before creping withinthe range from about 5 to 10 pounds per standard ream of 480 sheets,each 24 by 36 inches, and having a crepe ratio generally in the rangeHfrom 2.0 to 3.0, and containing a bonding agent in stated amounts.

The bonding agents which we prefer to use are liquid phenolformaldehydes. Other thermosetting resins such as urea-formaldehyderesins, melamine-formaldehyde resins, and resorcinal-formaldehyderesins, low pressure resins of the unsaturated polyester type (eg.diallyl phthalate), and a mixture of such thermosetting resins may alsobe used. Y

It is important that the resins employed be curable at a fairly rapidrate. Most desirably, the resins should be curable at temperatures andtimes employed in conventional equipment for scorching stereotype mats.With the present invention the linal drying and forming takes aboutthree minutes and cures the resin at aboutV 350 F. It will be apparent,however, that this temperature and time might be varied without anyundue inconvenience or serious loss of time.

It is not essential that the resin impregnant be completely watersoluble, as the resin can be introduced into the creped tissue sheets insolvents other than water or as a suspension of resin particles inwater. In some instances, it is preferable to use a nonaqueous liquidvehicle, asthere is less danger of reducing the bulk of the crepedtissue than in the case of an aqueous vehicle. However, it is importantthat the impregnant be rendered sufficiently tacky by Water to provideadequate adhesion between the several sheets and between the backing andthe mat or flong. In this respect, it is believed that best results canbe obtained with resins having a water tolerance or dilutability of fromL() part of water to 1.0 part of resin to 1.0 part of resin to 7.0 partsof water, by weight, in accordance with the standard dilutabilitytestsused in the art. Y

The resin content in the impregnated product may vary depending upon thephysical properties desired and the resin used. In general, for ourpurpose the product should contain from about l5 percentrto 75 percentby Weight of resin, with 40 to 50 percent being a particularlysatisfactory range. The percentage values mentioned are on the weight ofthe finished product on a volatile-free basis. After impregnation anddrying, the volatile content Aof the impregnated multi-ply materialpreferably should Vnot exceed about 15 percent by weight, on a bone drybasis, as impregnatedwebs having higher volatile contents are hardl tohandle Y and become sticky. A volatile content of from 5 to 9 percentappears to provide the Vbest results, although `volatile contents ofsubstantially lesser percentages may be satisfactory in certaininstances where the flexibility of the impregnated web is not'importantand where an adhesive is to be used for joining; theweb tothefstereotype mat. content of the material is determined by heating asample for 10 minutes at 160 C., and measuring the weight loss. 'Iltisloss, expressed as a percentage of the original weight, represents thevolatile content.

Perhaps a more sensitive and more accurate test for deter-mining aproper condition for the resin in the multiply backing material afterimpregnation and drying, if a water soluble resin is employed, is withreference to the Water solubility of the resin. Expressed in thismanner, it is preferable that the resin in the web after impregnationand drying be from 15 to 75 percent water soluble The volatile i'ndistilled water at 25 C. A water solubility of about 35% appears toprovide the best results, but a considerable lower solubility, or evenno water solubility, may be satisfactory if exibility is not importantand an adhesive is used for joining the web to the stereotype mat.

In a specific example, the backing was prepared by superposing twelvesheets of creped tissue made from chemical pulp, each individual sheethaving a drier basis weight of 5.9 pounds per standard ream of 480sheets, 24 by 36 inches, and a crepe ratio before impregnation ofapproximately 2.3. Thus the basis weight of the creped material wasapproximately 13.5 pounds per standard ream. The superposed sheets wereimpregnated by passage through a bath, aqueous or otherwise, containingthe resinous bonding agent. The excess liquid was removed by passing thewet superposed sheets through felt covered squeeze rolls using only suchpressure as would not change the structural characteristics of themulti-ply product or its individual plies. The impregnated sheets werethen dried by a current of hot air at a temperature of about 245 F. to325 F. The volatile content of the impregnated backing material at thisstage was approximately ll percent by weight. Material prepared in thismanner can be readily heat treatedto cure the resin dispersed throughoutthe plies of the material.

As normally practiced, the process of the present invention involvesapplying a relatively moist paperboard mat or llong of conventional typeto the upper surface of a lockup containing the printing elements to bereproduced, while at the same time providing a multi-ply backing sheetof paper of the type described over the paperboard mat. This backingsheet may be integral with the mat or separate therefrom. Suliicientpressure is then applied to the assembly by conventional procedures,which may involve the use of a pressure pad or cushion, to produce areproduction of the printing elements in the face of the mat. By thisoperation, the raised printing areas in the lockup become depressedareas in the face of the mat and the nonprinting areas in the lockupbecome raised areas in the mat.

After pressing, the mat and its associated backing are removed as aunit, and subjected to a drying operation in one or more steps. Dryingof the mat serves to eliminate substantially -all of the moisture in themat so that the moisture does not interfere with the casting operation,while forming the mat for casting. Further, the drying and formingoperation in connection with shrink-type mats serves to reduce the sizeof the mat to the particular dimensions required in the stereotypeplate. During the drying process, the temperature is maintained at asufliciently high value to set the resin in the backing to elfectpolymerization to such a degree that the resin no longer exhibits anysubstantial plastic flow under the temperatures and pressures of platecast- In FIGURE l, reference numeral indicates generally a printing formincluding the usual heavy metal chase 11 for containing the variouscomponents of the form, including the usual locking wedges of quoins(not shown) for holding the printing elements in place in the case.Substantially ush with the level of the chase 11 is an arrangement ofprinting elements which may include type slugs 12, each of whichcontains raised type faces 13 and engraving 14 separated from the type12 by means of a spacer 16 and a second set of type 17 with its raisedtype faces 18. A paperboard mat 19, which ordinarily contains from aboutl0 to 40 percent by weight of freeV moisture is shown superposed overthe printing form. Paperboard mats of this type commonly vary inthickness from about .024 to .040 inch. The mats are selected by a givennewspaper primarily on the basis of their shrinkage characteristics.Mats of the type now most generally used shrink considerably upondrying, depending in part upon their relative moisture content. Thisshrinkage occurs to the greatest degree transversely of the mat, atright angles to the machine direction of thev bers. The shrinkage in thelengthwise direction is ordinarily about half of what it is in the crossdirection.

ln newspaper work, it is common to use mats which provide from aboutone-half to about one and one-fourth inches in cross-wise shrinkage fora mat measuring about fifteen and nine-sixteenths inches wide andtwenty-one and three-quarter inches long between the limits of the typearea. In choosing a mat for the process of this invention where only onedrying step is used, it may be desirable to allow for a slight decreasein shrinkage Vover that ordinarily anticipated, so that where a givenmat may have a characteristic shrinkage of one and oneeighth inches, itwill shrink about one inch when combined with the backing materialdescribed. Where a conventional pre-drying step is employed, however,substantially all of the rated shrinkage in a given mat will be achievedby the end of the iinal drying step.

Disposed immediately over the mat 19, and coextensive ltherewith is apad or multi-ply sheet 21 composed of a plurality of bonded plies ofcreped cellulosic tissue or wadding impregnated with an unsetthermosetting resin, as previously described. For a mat having athickness of .024 to .040 inch and a moisture content of l0 to 40percent, the initial thickness of the wadding pad should be in the rangeof from about .030 to .100 inch. This is equivalent to a sheet of from 6to 20 plies of resin impregnated tissue, as described, having a basisweight per standard ream of about to 300 pounds and containing 40percent of resin on a bone dry basis. It may be desirable to use anon-impregnated tissue ply above the resin impregnated plies to avoidadherence between the backing and the molding combination.

Above the wadding pad 21 is a compressible cushion or moldingcombination 22 which may comprise a sheet of yieldable material such ascork, or mixtures of cork and synthetic rubber and/or fabric. In thisrespect it should be noted that the molding combination fairly wellregulates the pressure that is applied to the stereotype mat during themolding operation. The pressure on the mat will vary considerablybetween the printing and nonprinting areas because of the type `ofmolding cornbination selected and because of the space areas land depthsavailable in the lookup. Consequently, it will be seen that the moldingcombination is a matter of choice depending largely on the space-depthdesired in the mat and on the particular type of mat being used.

One example, of the numerous molding combinations which could beemployedincludes a sheet .070 inch thick consisting of a corkcomposition with a fabric facing, in combination with a fiberboard sheethaving a thickness of .090 inch. However, we have found that the moldingcombination can be eliminated in some cases.

In the practice of the invention by the use of the ma-l terialsdescribed in the foregoing, it will generally be found that goodadhesion is produced -between the mat and the plies of the backingmaterial. This is especially Atrue when the backing material contains amoisture sensitive resin and when the volatile content of the matmaterial is greater than about 4.0 percent.

In certain instances, however, it has been found desirable to provide anadditional layer of adhesive between the mat and the backing. Thisadhesive may be ofsuch nature that it adheres the mat and the backingprior to the molding operation, or the adhesive may be applied in suchmanner that it joins the mat and the backing only during the moldingand/or drying operations. For example, an adhesive may be applied to themat or to the backing, or to both, or the adhesive may consist of aseparate film or an impregnated carrier sheet adapted for insertion intothe lay-up assembly between the mat and the backing.

The adhesive coating 20a is preferably a uniform film of a moisturesensitive adhesive material, such as sodium acrylate, .Methocel, amethyl cellulose sold by Dow Chemical Co. or polyvinyl alcohol, in orderthat it will 35cm-eee.

be' tacky during the' formation of the combined mat and backing' whenthe moisture in the mat is drawn into the backing', ,or it may be apressure sensitive material which will bond the backing to the matduring the molding operation. Further, the adhesive should be moisturepermeable,l so that it does not act as a barrier to the moisture in themat 19a asV this moisture seeks to penetrate the backing 21a? Theadhesive selected for joining. the mat to the backing should preferablybe one which is suciently tacky to provide a good bond between the matand the backing during the molding of the composite stereotype mat.Otherwise, the subsequent drying operation might de form the hacking asit receives moisture from the mat and cause uneven shrinkage' of 4thetwo resulting in their getting out ofregister with eachother.

If desired, a film or carrier sheet may be used for thc adhesive lmv29u. However, in such instance it is desirable that the carrier sheetbe capable of distortion in order to conform withV the mat and backing.For this reason a' soft tissue or a non-woven fabric might be used.

ItV is possible that by using an added adhesive layer, asdescribedabove, a somewhat smaller amount of resin might be used in the backing,since this resin content is no longer relied on for adhering the backingto the mat in the manner previously described. It is also possible thatit may be desirable in certain instances to use a heated pressure rollin the molding operation, in order to better set the adhesive andthereby improve the hond- -ing between the mat and backing.

With reference now particularly to FIGURES, it is seen that. theprinting form 1d with the mat, backing, and blanket in place is set onthe table 23 and passed between the nip'of pressure rolls 24 and 26. Oneor both of the rolls 2d and Ztris made vertically adjustable tocompensate for different thicknesses of printing forms. The pressures ofmolding used in our process are substantially the same as those usedpresently in molding stereotype mats. Itis difficult to measure theexact pressure employed, as the contacting areas of roll to which thepressure is applied cannot be` ascertained accurately. However, it'. isgenerally accepted that the molding pressures 'required lfor goodreproductionV are on the order of: 2,000to 4,030 pounds per square inchover `theV printing areas and maybe considerably higher.

The'use of aroller moldingl'm'achine comprising a chase-supporting bedand a pair of rotatable pressurev rolls is by far the most common methodof molding mats, but the process of the present invention is equallyapplicable to molding procedures invoiving the use of direct pressurewith flat platens. I

As pressure is applied to theassembly shown in FIG- URE 3, themat i9 iscompressed into the spaces be-Y tween the raised printing characters andk*forms a sharply deiined reproduction of the printing characterscontained in the lookup or form 16. The porous backing 2i is alsocapable of absorbingy any moisture expressed from the mat 19. The'backing 2i is considerably more compressible than the mat 19 and, as aresult of the pressing, the thickness of the backing 2i is considerablyreduced over the printing areas. Under ordinary molding pressures, the'thickness may be reducedy by a factor of four or-ve times over the'printing areas, so that a backing originally .05() inch in thicknessVmay-end up as a compressedV backingof about .01() inch, whereas in thenonprinting areas .the bulk is compressed toabout .040 inch, therebyproviding a space depth between the level of the non` printing areasland the base of the printing areas of about .030`vinch.` Thus ino-neoperation the mat is molded and completely packed simultaneously andmore rapidly than is possiblein a hand packing operation. Furthermore,with the described invention, the molded depth retention in half toneareas is better than ina hand packed mat.

The backing material is such that its face is able to conform accuratelyto the contour of the back of' the"- mat i9 duringV application ofpressure. AAt the same time the backing .becomes quite securely bondedto vthe back of the mat i9 over the areas of the4 mat subiectedjto highmolding pressures. In ins'tauceswhere the glue line or adhesiyeoating'pZtla' isnotrelied onto b'ond the backing to the mat, thisbonding is effected either because of the adhesive properties ,of theresin contained in the backr ing, or it may be partly ldue toagmechanical' locking of the printing areas at the back of the' matinthe collapsed arcas' of the backing immediately overlying theseareas ofthe mat. With the use of the adhesive coating' 20a the pressure on themat duringv the molding operation causes the back tov be bonded to themat. With a moisture sensitive adhesive this bonding is effected by theexpression of moisture in the mat toward the adhesivey to thereby renderthe latterV suciently tacky to bond the hacking tothe mat.

K A portion of the backed mat after removal from the molding apparatusis illustrated in enlarged form in FGURE 4.' mat 19 is depressed inc'onforrnityvto the shape of the lookup, as seen at 28 and 29, dependingon the pressure, molding combination, and the space areas and depthsavailable in the original lookup. l

in the nonprinting areas, as for example in.- the area 29, theremarkableresiliency, of the backing 2i causes the backing-to recovermuch of its original vthickness after removalVV of the moldingpressure',` vas indicated Vat numeral 33;. Yet in the areas above theprinting surfaces, such as the area 31, Vthe backing takes amorepermanent set but still retains a high degree ofhiiexibility` andmoisture permeability. The-result is that the backed` mat produced bythe molding operation has a generally` planar rear surface 35 which mayb e readily conformedto the surface of the dryer. Further, the backingmaterial is packedy into those small nonprinting areas that a handpacker does not even touch in the ordinary processk of stereotype matvforming. Consequently, lthere is pro` vided by the backing a properarrangement of bulkfor resisting collapsing of the mat during subsequentsteps in the formation of the tinished stereotype matrix.

Afterthe remoyal from the molding apparatus, the composite mat andbacking is then ready for drying and for setting of the resin. For themanufacture of curved stereotype plates, rthe mat 19 and its backingrZlare given a uniform curvature by introducing the mat into a conventionaldryer'assembly illustrated in FIGURE 5. The particular dryer illustratedin the drawings consists of an asbestos covered drum 34 in which aplurality of heating elements 36 are disposed beneathy the asbestossurface. A cover or chamber 37 having arperfrorated inner face 38ishinged tothe base 34 at 'a hinge 39. The backed mat is held againstthe inner face 33 by applying a vacuum to the back of the composite matthrough the perforations in the face 38; The cover is also heatedV bymeans of spaced heating elements 40 contained therein. As previouslystated, the multi-ply pad of resin-.impregnated tissue sheets mayVinclude one unimpregnated ply on theupper surface thereof.V K

The Avacuum applied to theVmat-holds the mat in con-Y tact with the facetand spaces the face of the mat slightly from the rasbesto-s covered1surfaceof the base 34 when the cover 37 is in its closed position. Thusthe vacuum serves not only to hold the mat in position but, also, formsthe back of the mat in a smooth surface so as to provide a uniformlycurved reference surface for the mat. The temperature at the base of thescorcher is ordinarily on the order of 250 to 400 F. As the heat isapplied, the moisture is driven from the mat and this moisture passesthrough the porous backing material and is there-Y upon vented. Itisimportant that the resin selected should not become cured` or rigiduntil substantially all of the desiredvshrinkage of the mat and backinghas taken place. Consequently, the resin should be one which will becomeAs seen in that drawing, the face of theV g cured throughout at atemperature somewhere near the upper range of the scorcher temperaturewhich will prevail throughout the mat when` essentially all of themoisture has been drawn therefrom. The resins mentioned above have thesecharacteristics and mats packed with these types of dispersed resinproducts do not evidence any tendency to crack or warp during casting ofthe stereotype plate.

Where only one drying step is used, a treatment time of 2 to 5 minutesat temperatures of 300 F. to 400 F. will suiiice to drive olf themoisture and set the resin sufficiently under moisture conditionsnormally prevailing in that mat. The control of shrinkage is facilitatedby operating at a lower vacuum, on the order of one and onehalf inchesof mercury during the first minute or two and then increasing it to avalue of 5 to 6 inches of mercury when substantially all of the moisturehas been driven off. And, as previously mentioned, substantially all ofthe moisture is driven oft before the resin in the backing is set and,therefore, such resin content does not intefere with the shrinkage ofthe mat and backing as a unit. Where a pre-drying step is employed inconjunction with a final drying and forming, times of about 40 to 80seconds at temperatures of about 150 to 250 F. may be employed toinitiate shrinkage of the composite mat without substantial setting ofthe resin. In this latter respect, it should be noted that there aredefinite advantages in some instances in utilizing a pre-drying stepbefore finally forming the mat. The pre-drying operation helps torigidify the backing so that it is better able to resist the vacuumpressure in the final dryer and prevent an undesirable collapsing of theuncured mat under such pressure. Further, this pre-drying of the mat andbacking is an aid in providing better space-depth characteristics insome instances.

The resin in the backing should be cured suliiciently during the finaldrying operation to a point wherein it will resist collapse under thetemperatures and pressures encountered in the casting of the stereotypeplate. Our experience indicates that in the case of aphenol-formaldehyde resin a cure of at least 85 percent should beachieved. Expressed alternatively, the resin extractibles in the sheetshould not exceed about 15 percent. The extractibles content can bereadily determined by the standard A.S.T.M. test (13494-41) whichinvolves taking a known weight of typical sample of the cured sheetmaterial in finely comminuted form, and placing this sample in a Soxhletapparatus where it is extracted with hot acetone for a period of fourhours. The acetone is then evaporated under controlled conditions andthe sample removed, so that the residue constitutes the extractiblematerials which have been dissolved by the acetone.

Upon removal of the backed mat from the scorcher, the mat is ready forinsertion in the casting box. The final form of the mat is illustratedin FIGURE 6 of the drawings and includes the paperboard mat 19 having acasting face i9b of concave shape and the backing 21 in which thethermosetting resin has become set and rigidified by the heat treatmentin the dryer. Composite mats of this type have been found to adequatelyresist collapse under type casting pressures on the order of l5 to 25pounds per square inch.

The process described can be very conveniently carried out onconventional stereotype forming equipment with little or no change inthe present procedures or equipment and, when so used, it realizes mostimportant savings in time and labor as well as producing an improved matand, consequently, a better printing plate.

There are a number of factors which should be considered in the practiceof the invention in order to achieve the best results in the molding ofthe composite mat and backing. These include (l) the degree of crepingin the individual unimpregnated tissue plies constituting the backingmaterial; a crepe ratio of between 1.3 and 2.5 is preferred, (2) theamount of stretch in the backing after l@ impregnating and drying shouldbe between 20% and 60% in the machine direction, based on the originallength of the sample of backing, (3) the resin content in the backing,which is preferably 40 to 50 percent by dry weight of the finishedproduct on a volatile free basis, but which may be within a range of 15to 75 percent and still be effective in certain instances, (4) thethickness or bulk of the backing, preferably .030 to .100 inch beforethe composite mat is formed in the case of newspaper mats, (5) the Watersolubility of the resin in the backing after impregnation and dryingwhich is desirably about 35%, in the event a water soluble resin isused,

(6), the percentage of volatiles in the backing after the composite webis formed, indicated above as being preferably no greater than 15percent of the resin content, with a range of from 5 to 9 percent beingdesired for most practical uses, (7) the type of molding combinationemployed, and (8) whether a single or multiple step, nonshrink orshrinkage process is desired in forming the stereotype mat or matrix. Itwill be understood of course, that the thickness of the mat will belargely a matter of convenience. While all of the above mentionedfactors play a part in providing the improved stereotype mat madepossible by this process, a proper balancing within the various rangesdisclosed herein should be achieved to obtain the finest qualityreproduction.

The foregoing discussion has dealt primarily with the backing of curvedstereotype mats of the high shrink type now commonly employed innewspaper work. The numerous advantages of the new combination can alsobe realized in related fields. As previously indicated, the mat andbacking can be pressed between flat platens, and the resulting backedmat after curing of the resin and shrinkage of the mat can be employedfor making flat castings. Alternatively, the molding, curing, andshrinkage may be part. of the same operation, by employing heated,perforated platens in the fiat molding press.

For another example, advertising agencies distribute the so-called admats to numerous newspapers throughout the country. These mats arecommonly of the noshrink type and are intended to provide a mold forreceiving a iiat casting of metal or for direct casting in newspaperwork. The casting is then inserted into a newspaper page lockup alongwith the remaining printing elements, and a high shrinkage mat is thenmolded on this lockup. The described backing can also be employed as abacking for the no-shrink type mat. In this type of application, theresin in the backing is convenienty cured at the time the mat is moldedby using heated platens in a direct pressure molding assembly, and themat and its attached backing may then be distributed to the variousnewspapers.

Another field in which mats of little or no shrinkage are commonlyemployed is that of color reproduction. Normally, color printing systemsinclude a series of as many as four printing rolls, one for each ofcolors desired, so that a plurality of stereotype plates must beprovided for each printed page. In this field, it is essential thatthere be perfect registry between the printing surfaces, soit is commonpractice to use a no-shrink mat for preparing each of the plates.Because of its inherent ability to con-.` form exactly to the mat duringdrying the backing material of the present invention has especialutility in the manufacture of such mats.

It will be evident that various modifications can be made in thedisclosed examples without departing from the scope of the presentinvention.

1. The method of making a stereotype mat which comprises applying onto aprinting form a relatively moist paperboard mat having a moisturecontent in the range from 10 to 40 percent by weight and -a multi-plybacking superimposed thereon, said backing comp-rising a moldable sheetcontaining a plurality of plies of creped tissue having an unsetthermosetting resin dispersed therein, the

1 i resin content` in said backing to 75 percent by weight of said sheeton a dry basis, said backing sheet having a volatile content in therange from 5 to 15 percent by weight on a bone dry basis, applyingsuliicient pressure to the resulting assembly to form an impression ofthe p-rinting areas of said printing form into said mat, removing saidassembly from said printing form, drying said backing and said mat whileapplying a re-V duced pressure Vat the rear of said backing so that themoisture in said mat is vented through said backing, and heating saidmat and said backing under conditions suiiicierit to cure the resin insaid backing to withstand the pressures encountered in stereotypecasting.

2,. The method of making a stcreotype'mat which comprises applying ontoa printing form a relatively moist paperboard mat having a moisturecontent in the range from to 40 percent by weight and a multi-plybacking superimposed thereon, said backing comprising a moldable sheetcontaining a plurality of plies of creped tissue having an unsetthermosetting resin dispersed therein, the resink content in saidbacking sheet constituting from to 75 percent by weight of said sheet ona dry basis, said backing sheet having a volatile content in the rangefrom 5 to 15 percent by weight on a bone dry basis, applying suilicientpressure to the resulting assembly to form an impression of the printingareas of said printing form into said mat, removing said assembly fromsaid printing form, drying said backing and said mat so that themoisture in said mat is expelled, and heating said mat and said backingunder conditions sufficient to cure the resin in said backing towithstand the pressures encountered in stereotype casting.

3. The method of making ak stereotype mat which comprises applying ontoa printing form a .relatively moist paperboard mat having a moisturecontent in the range from l0 to 40 percent by weight and multi-plybacking superimposed thereon, said backing comprising a moldable,moisture-permeable sheet containing a plurality of plies of creped,cellulosic tissue having an unset thermosetting resin dispersed therein,said backing sheet containing from 15 to 75 percent by weight of saidresin on a dry basis, said backing sheet having a volatile content inthe range troni 5 to lSpercent by weight on a bone dry basis, applyingysuilicient pressure to the resulting assembly to form an impression ofthe printing areas of said printing form onto said mat, removing saidassembly from said printing form, drying said mat and said backing underconditions suicient to permit shrinkage of said mat and backing to apredetermined degree, and heating said mat and' said backing attemperatures sufficient to cure the resin in said backinv.

4. The method lof making a stereotype mat which comprises` applying ontoa printing form a paperboard mat having a free'moisturecontent in therange from 15 to 40 percent by Weight and Va multi-ply backing sheet orpad superimposed thereon, said backing comprising a plurality of pliesof creped paper bonded together by an unset thermosetting compositiondistributed through. said plies and having an initial thickness in therange of from about 0.030 to 0.100 inch and being moisture permeable,the resin content in said backing material constituting from 15 to 75percent by-weight of said backing material, said backing sheet having avolatile content in the range from 5 to 15 percent by weight on a bonedry basis, applying sufficient pressure to said mat andy said backingwhile in superimposed relation over said form to form an impression ofsaid form in saidmat, removing said mat and backing material as anassembly from said printing form, and thereafter drying said mat andsaid backing at a temperature sufficient to dry said mat into asubstantially moisture-free Kcondition and'to cure the resinouscomposition in said backing material.

5; The method of making a stereotype mat which cornprises impregnatingla Vplurality of plies of creped, cellulosic tissue with an unsetthermosetting resinous compo sheet constituting from 15' sitiondispersed in a liquid vehicle, drying the impregnated material toprovide a laminated, moisture-permeable backing material having resinparticles dispersed therein in sufficient quantities to provide a resincontent of from l5 to 75 percent by weight in said backing material,said backing material having a volatile content in the range from 5 tol5 percent by weight on a bone dry basis, superimposing said backingover a paperboard mat with `an adhesive film therebetween, saidpaperboard mat having a moisture content from 10 to 40 percent byweight, laying the resulting backed mat over a series of printingelements with the paperboard portion thereon in contact with saidelement, applying suiicient pressure to make an impression of saidprinting elements in said paperboard, removing said backed mat from saidprinting elements, and thereafter drying said backed mat by theapplication thereto of heat, While simultaneously removing moisturevapor from said mat through said backing material, at a temperaturesuilcient to dry the backed mat to cure the resin in said backingmaterial sufficiently to withstand the pressures encountered instereotype casting.

6. A stereotype matrix comprising a molded iiong and a molding blanketsecured thereto and providing a backing for said flong, said moldingblanket including a cured thermosetting resin impregnated fibrous sheet,the free surface of said ong having the printing matter molded thereinand the contacting surfaces of said blanket and said ilong beingcontoured in the non-printing areas, the free surface of said moldingblanket being flat.

7. A sterotype matrix comprising a molded ong and a molding blanket injuxtaposition, and a Vquantity of adhesive between said flong and saidmolding blanket adherring said molding blanket to said ong, said moldingblanket including a sheet of fibrous material impregnated with a curedphenolic resin, the free surface of said ong having printed mattermolded therein and the contacting surfaces of said sheet and said flongbeing contoured in the non-printing areas, and the free surface of saidmolding blanket being flat.

8. A stereotype matrix comprising a molded flong and a molding blanketin juxtaposition, and a layer of adhesive between said flong and saidmolding blanket adhereing said molding blanket to said ong, said moldingblanket consisting substantially of a layer of paper sheet materialimpregnated with a cured phenolic resin, the free surface of said flonghaving printed matter molded therein yand the contacting surfaces ofsaid blanket and said ong being contoured in the non-printing areas, thefree surface of said molding blanket being ilat.

9. A stereotype matrix comprising a molded ong and a molding blanket injuxtaposition, and a layer of adhesive between said ong and said moldingblanket adhering said molding blanket to said iiong, said moldingblanket consisting substantially of a layer of paper sheet materialimpregnated with a cured phenol formaldehyde resin, the free surface ofsaid ilong having printing matter molded ytherein and the contactingsurfaces of said blanket and said Hong being contoured in thenon-printing areas, the free surface of said molding blanket being flat.

l0. A stereotype matrix comprising a molded flong and a molding blanketin juxtaposition, and a layer of adhesive between said flong and saidprinting blanket adhering said molding blanket to said ong, said moldingblanket consisting substantially of a layer of paper sheet material.having a maximum thickness of between about 0.035 inch `and about 0.040inch and impregnated with a cured phenol formaldehyde resin, the resinconstituting about 50% by Weight of the impregnated sheet, the freesurface of said flong having printing matter molded therein and thecontacting surfaces of said blanket and said ong being contoured in thenon-printing areas, the free surface of said molding blanket being flat.

(References on feilowing page) References Cited in the file of thispatent UNITED STATES PATENTS Annand May 27, 1909 Baekeland July 17, 19175 Novotny Nov. 22, 1921 Schroger Jan. 27, 1925 Hole Aug. 27, 1929Cochran et a1 May 29, 1934 Matuschke et a1. May 26, 1936 10 Morgan etal.Feb. 9, 1937 14 Catlin Mar. 15, 1938 Rowe Mar. 14, 1944 Baker Dec. 27,1949 Catlin et a1 May 29, 1951 Germain Mar. 4, 1952 Richardson Mar. 1,1955 Schaum NOV. 27, 1956 FOREIGN PATENTS Germany June 11, 1928

1. THE METHOD OF MAKING A STEREOTYPE MAT WHICH COMPRISES APPLYING ONTO APRINTING FROM A RELATIVELY MOIST PAPERBOARD MAT HAVING A MOISTURECONTENT IN THE RANGE FROM 10 TO 40 PERCENT BY WEIGHT AND A MULTI-PLYBACKING SUPERIMPOSED THEREON, SAID BACKING COMPRISING A MOLDABLE SHEETCONTAINIG A PLURALITY OF PLICES OF CREPED TISSUE HAVING AN UNSETTHERMOSETTING RESIN DISPERSED THEREIN, THE RESIN CIONTENT IN SAIDBACKING SHEET CONSTITUTING FROM 15 TO 75 PERCENT BY WEIGHT OF SAID SHEETON A DRY BASIS, SAID BACKING SHEET HAVING A VOLATILE CONTENT IN THERANGE FROM 5 TO 15 PERCENT BY WEIGHT ON A BONE DRY BASIS, APPLYINGSUFFICIENT PRESSURE TO THE RESULTING ASSEMBLE TO FORM AN IMPRESSION OFTHE PRINTING AREAS OF SAIID PRINTING FORM INTO SAID MAT, REMOVING SAIIDASSEMBLE FROM SAID PRINTING FORM, DRYING SAID BACKING AND SAID MAT WHILEAPPLYING A REDUCED PRESSURE AT THE REAR OF SAID BACKING SO THAT THEMOISTURE IN SSID MAT IS VENTED THROUGH SAID BACKING, AND HEATING SAIDMAT AND SAID BACKING UNDER CONDITIONS SUFFICIENT TO CURE THE RESIN INSAID BACKING TO WITHSTAND THE PRESSURES ENCOUNTERED IN STEREOTYPECASTING.
 6. A STEREOTYPE MATRIX COMPRISING A MOLDED FLONG AND A MOLDINGBLANKET SECURED THERETO AND PROVIDING A BACKING FOR SAID FLONG, SAIDMOLDING BLANKET INCLUDONG A CURED THERMOSETTING RESIN INPREGNATEDFIBROUS SHEET THE FREE SURFACE OF SAID FLONG HAVING THE PRINTING MATTERMOLDED THEREIN AND THE CONTACTING SURFACE OF SAID BLANKET AND SAID FLONGBEING CONTOURED IN THE NON-PRINTING AREAS, THE FREE SURFACE OF SAIDMOLDING BLANKET BEING FLAT.